I'm having the same problem all day long:lfd: (eximsyntax) Exim syntax errors from x.x.x.x : 15 in the last 3600 secs
and I'm not finding the /var/log/exim_mainlog and there are many pc's in my lan, because of that I'm not able to scan all of them now trying to find viruses, or malwares.
Are there another way to find the cause? more efficiently or precisely without contact the host.